Miniaturized multiband antenna

ABSTRACT

The invention relates to an antenna comprising a dielectric substrate ( 1 ) and two resonant printed wiring structures, more particularly for use in high-frequency and microwave domain. On an end face of the structure ( 2 ) is arranged along a first edge and on an opposite, second edge of the same end face a second printed wiring structure ( 3 ). The arrangement of the printed wiring structures provides that resonances are developed which make the use of the proposed antennas in the four separate GPS, DCS/PCS, UMTS and Bluetooth applications possible.

The invention relates to an antenna comprising a substrate having atleast one resonant printed wiring structure, more particularly formobile dual or multiband telecommunication sets such as mobile andcordless telephones, as well as appliances communicating according tothe Bluetooth standard. The invention further relates to a circuit boardwith such an antenna as well as a radio communication device having suchan antenna.

In mobile telecommunication, electromagnetic waves in the microwavedomain are used for transmitting information. Examples for this are themobile telephone standards in the frequency ranges from 890 (880) to 960MHz (GSM900), from 1710 to 1880 MHz (GSM1800- or DCS), as well as from1850 to 1990 MHz (GSM1900 or PCS), further the UMTS band (1885 to 2200MHz), the DECT standard for cordless telephones in the frequency rangefrom 1880 to 1900 MHz, as well as the Bluetooth standard in thefrequency range from 2400 to 2480 MHz, which serve to exchange databetween various electronic devices such as, for example, mobiletelephones, computers, entertainment electronic appliances etc. Besidesthe transmission of the information, additional functions andapplications such as, for example, for satellite navigation in the knownGPS frequency range (1573 MHz) are also realized at times.

Contemporary telecommunication devices of this type are therefore to bein a position to be operated in as many of said frequency ranges aspossible, so that corresponding dual or multiband antennas are necessarywhich cover these frequency ranges.

For the purpose of transmission and reception the antennas have to haveelectromagnetic resonances at the respective frequencies. To minimizethe size of the antenna for a given wavelength, generally a dielectrichaving a dielectric constant ε_(r)>1 is used as a basic module of theantenna. This leads to a shortening of the wavelength of the radiationin the dielectric by a factor 1/{square root}{square root over (ε _(r))}. An antenna designed on the basis of such a dielectric thereforebecomes smaller by this factor.

An antenna of this type thus comprises a block (substrate) of dielectricmaterial. On at least one of the surfaces of the substrate are depositedone or various metallizing structures depending on the desired operatingfrequency band or bands. The position or the resonant frequencies dependon the dimensions and the arrangement of the printed metallizationstructure and also on the value of the dielectric constant of thesubstrate. The individual resonance frequencies then shift to lowerfrequencies as the values of the dielectric constant rise.

In DE 10049845 is described a microwave antenna having a dielectricsubstrate and at least one resonant printed wiring structure which ischaracterized in by a plurality of line sections. The line sections havein essence a meander form on various side surfaces of the substrate.Such antennas can be welded on a printed circuit board together withother components via customary surface mounting. The bandwidth of such aknown antenna is only sufficient to achieve a complete covering of thefrequency bands of the GSM standard. The multiband applicationsmentioned in the opening paragraph are thus not possible.

It is an object of the invention to provide an antenna for saidmultiband applications.

The object is achieved by an antenna of the type defined in the openingparagraph in that the substrate on one end face has a first printedwiring structure along a first edge and a second printed wiringstructure on an opposite, second edge of the same end face.

In addition to the advantage of the possibility of surface mounting(SMD), the antenna has the considerable advantage that the antenna canbe used in the frequency ranges of the UMTS and Bluetooth standards. Aparticular advantage of the antenna is that the bandwidth of the antennadespite its small size is more than 1 GHz. A further considerableadvantage is that the resonant metallization structures can completelybe deposited on only one of the end faces of the substrate and thus thecomplete metallization structure can be manufactured in onemanufacturing step.

The second printed wiring structure of the antenna is equal to the firstprinted wiring structure as regards shape and size. The substrate of theantenna is, in essence, oblong with two larger end faces and foursmaller side faces. The first and second printed wiring structures aredeposited on a first end face and stretch out from a first to a second,opposite side face along the edge.

The first and second printed wiring structure have the form of arectangular face.

Each printed wiring structure may also be subdivided into four printedwires, a first printed wire extending from the first to the second sideface along the edge, a second printed wire extending from the second tothe first side face, a third printed wire extending to the first printedwire and the first printed wire connecting to the second printed wire. Afourth printed wire then connects to the second printed wire.

In this further embodiment the antenna can be operated in the frequencyranges of the GPS, DCS, UMTS and Bluetooth band.

The first and second printed wires as well as the third and fourthprinted wires of the antenna are about equally long. At the same timethe first and second printed wires are longer than the third and fourthprinted wires. The fourth printed wire runs along an edge of the firstend face. The first and third printed wires run perpendicular to thesecond and fourth printed wires. The two printed wiring structures aremirrored on the first end face.

The invention also relates to a printed wiring board on which an antennaaccording to the invention is mounted, as well as a radio communicationsdevice, more particularly for the GPS, DCS, UMTS and Bluetooth rangewith an antenna according to the invention.

These and other aspects of the invention are apparent from and will beelucidated, by way of non-limitative example, with reference to theembodiment(s) described hereinafter.

In the drawings:

FIG. 1 gives a diagrammatic representation of a first antenna accordingto the invention;

FIG. 2 a reflection diagram measured at the first antenna;

FIG. 3 a diagrammatic representation of a second antenna according tothe invention;

FIG. 4 a reflection diagram measured on the second antenna;

FIG. 5 a diagrammatic representation of a third antenna according to theinvention; and

FIG. 6 a reflection diagram measured on the third antenna.

The embodiments to be described hereinafter have a substrate in the formof an in essence rectangular block whose height is about a factor of 3to 10 smaller than its length or width. On the basis of this, therespective upper or lower (large) faces of the substrate in therepresentations of the Figures are referred to as upper or lower endfaces respectively and the faces perpendicular thereto are referred toas side faces in the following description.

As an alternative, it is also possible to choose instead of arectangular substrate other geometric forms such as, for example, acylinder form on which a respective resonant printed wiring structurewith a, for example, helical pattern is deposited.

The substrates can be manufactured by embedding a ceramic powder in apolymer matrix and have a relative permittivity of ε_(r)>1 and/or apermeability of μ_(r)>1.

The first antenna shown in FIG. 1 comprises a dielectric substrate 1 onwhose lower end face are deposited two printed wiring structures 2 and3. The printed wiring structure 2 will be supplied with power via afirst supply 4, on the other hand, the printed wiring structure 3 isconnected to a second supply 7. The substrate 1 is welded on a printedcircuit board (PCB) 5 by surface mounting (SMD). This is effected by aflat welding in which several welding points not shown here (so-calledfootprints) and the supply 4 are connected to the board. The supply 4 isthen brought into contact with a printed wire 6 on the board 5 via whichradiating electromagnetic energy is supplied as a signal. The supply 7,on the other hand, is connected to a ground metallization 8 of thecircuit board 5.

The two printed wiring structures 2 and 3 are arranged symmetrically onthe lower end face of the substrate 1. Each printed wiring structure ofthe first antenna comprises a single printed wire which is impressed onthe substrate 1 and runs parallel along the length of the lower end facefrom one side face to a second, opposite side face of the substrate 1.

The resonant frequencies of this antenna may be set in known fashionover the length and width as well as the distance of the impressedprinted wiring structure. Superpositioning of the resonant frequenciescaused by the printed wiring structures results in a bandwidth whichenables the antenna to be operated at the desired frequencies.

For a possible production of this first antenna the dimensions of thesubstrate 1 are about 8×8×2.0 mm³. The material selected for thesubstrate 1 has a relative permittivity of ε_(r)=21.5 and a tanδ=1.17×10⁻⁴. This about corresponds to the HF properties of a commercialNP0-K21 ceramic (Ca_(0.05)MG_(0.95)TiO₃ ceramic). The printed wire wasmanufactured by means of silver paste. The width of the line section isabout 0.5 mm.

FIG. 2 shows the ratio R measured on the supply 4 of this antennabetween the power reflected by the antenna and the power supplied to theantenna (reflection coefficient) plotted against frequency f in Hz. Itmay be clearly noticed that one of the two resonances covers thefrequency range of the Bluetooth band from 2400-2483.5 MHz. The readbandwidth of over 1 GHz is sufficient to be able to effectively workwithin the frequency band. A further resonance is found at about 3100MHz.

In addition to the advantage of the possibility of surface mounting(SMD) which holds for all embodiments, this embodiment has theconsiderable advantage that the antenna can be operated in thefrequencies of the Bluetooth band. A further considerable advantageconsists in that the resonant metallization structures 2 and 3 can becompletely deposited on only one of the end faces of the substrate 1 andthus the manufacture of the complete metallization structures 2 and 3can be integrated in one manufacturing step.

FIG. 3 shows a second embodiment of the invention. In thisrepresentation like or corresponding elements and components to thoseshown in FIG. 1 are referred to by like reference characters. As far asthis is concerned, the description is referred to in conjunction withFIG. 1 and hereinafter only the differences will be explained.

With a production of this second antenna the dimensions of the substrate1 are about 12×12×2.0 mm³. The material chosen for the substrate 1 isalso an NP0-K21 ceramic having a relative permittivity of ε_(r)=21.5 anda tan δ=1.17×10⁴. Printed wires were also manufactured with silverpaste. The width of the printed wires was changed by about 1.0 mm.

The advantages of the second embodiment consist of the integration ofthe manufacturing of the metallization structure in one step as well asthe possibility of surface mounting. This antenna, however, has thesubstantial advantage that it can be operated at the frequencies of theUMTS and Bluetooth standard.

FIG. 4 shows the ratio R measured at the supply 4 of this antennabetween the power reflected by the antenna and the power supplied to theantenna (reflection coefficient) plotted against frequency f in Hz. Tworesonant frequencies may clearly be read at about 1.95 GHz and 2.6 GHz.The bandwidth of the second antenna is much beyond 1 GHz, so thatfrequencies both in the UMTS as well as Bluetooth band can be covered.

FIG. 5 shows a third embodiment of the invention. The third antenna alsocomprises a dielectric substrate 1 on whose lower end face the twoprinted wiring structures 2 and 3 are deposited. The essentialdifference between the printed wires 2 and 3 and the first antenna liesin the form of the printed wires. Furthermore, the printed wiringstructure 2 will be supplied with power via a first supply 4, on theother hand, the printed wiring structure 3 is connected to a secondsupply 7. The same or corresponding elements and components of theantenna shown in FIG. 5 are referred to by the same reference charactersused in FIG. 1. As far as this is concerned, the description relating toFIG. 1 is referred to and only the differences will be explainedhereinafter.

The metal structures 2 and 3 are formed not only by a first printed wire11 which runs along the length of the lower end face from the first sideface to the second, opposite face of the substrate 1, but also by asecond, inner printed wire 12 which runs parallel to the first printedwire 11 at a distance of about 0.8 mm.

The two parallel printed wires 11 and 12 are connected by a thirdprinted wire 13 running perpendicularly to the printed wires 11 and 12along the second side face. A fourth printed wire 14 also runsperpendicular to the printed wires 11 and 12 and is connected to theprinted wire 12. It stretches out along the first side face of thesubstrate 11 in the direction of the printed wire 11. Different from theprinted wire 13, the printed wire 14 does not connect the parallelprinted wires 11 and 12. Printed wires 11 to 14 together form the metalstructure 9 or 10, respectively.

The dimensions of the substrate 1 of the third antenna are about12×12×2.0 mm³. The material selected for the substrate 1 also comprisesan NP0-K21 ceramic having a relative permittivity ε_(r)=21.5 and a tanδ=1.17×10⁻⁴. Printed wires were also produced by means of silver paste.The width of the printed wires 11 to 14 was changed to about 0.5 mm.

A special advantage of this embodiment is thus in addition to theadvantages mentioned above that with this antenna multiband operation ofa respective mobile radio is possible.

FIG. 6 shows the ratio R between the power reflected by the antenna andthe power applied to the antenna (reflection coefficient) measured atthe supply 4 of the third antenna plotted against frequency f in GHz.Three resonant frequencies at 1.57 GHz, 1.85 GHz and 2.55 GHz and abandwidth of the antenna of about 1.2 GHz can clearly be recognized. Thecondition of the resonances makes it possible to utilize the proposedantennas in the four separate applications GPS, DCS/PCS, UMTS andBluetooth.

1. An antenna having a dielectric substrate (1) and two resonant printedwiring structures, more particularly for use in high-frequency andmicrowave range, a first printed wiring structure (2) being arranged onone end face of the substrate (1) along a first edge and a secondprinted wiring structure (3) on an opposite, second edge of the same endface.
 2. An antenna as claimed in claim 1, characterized in that thesecond printed wiring structure (3) is equal to the first printed wiringstructure (2) as regards shape and size.
 3. An antenna as claimed inclaim 1, characterized in that the substrate (1) is in essencerectangular having two larger end faces and four smaller end faces andin that the first and second printed wiring structures (2, 3) aredeposited on a first end face and stretch out from a first to a second,opposite side face along the edge.
 4. An antenna as claimed in claim 1,characterized in that the first and second printed wiring structures (2,3) have the form of a rectangular face.
 5. An antenna as claimed inclaim 3, characterized in that each printed wiring structure (2, 3) issubdivided into three printed wires (11 to 13) where a first printedwire (11) stretches out from the first to the second side face along theedge, and a second printed wire (12) stretches out from the second tothe first end face, a third printed wire (13) is connected to the firstprinted wire and the first printed wire is connected to the secondprinted wire.
 6. An antenna as claimed in claim 5, characterized in thata fourth printed wire (14) is connected to the second printed wire (12).7. An antenna as claimed in claim 5, characterized in that the first andsecond printed wires (11, 12) are equally long.
 8. An antenna as claimedin claim 5, characterized in that the third and fourth printed wires(13, 14) are equally long.
 9. An antenna as claimed in claim 5,characterized in that the first and second printed wires (11, 12) arelonger than the third and fourth printed wires (13, 14).
 10. An antennaas claimed in claim 5, characterized in that the fourth printed wire(14) runs along an edge of the first end face.
 11. An antenna as claimedin claim 5, characterized in that the first and third printed wires arearranged perpendicular to the second and fourth printed wires.
 12. Anantenna as claimed in claim 2, characterized in that the second printedwiring structures (2, 3) are mirrored on the first end face.
 13. Aprinted wiring board on which an antenna as defined in claim 1 isarranged.
 14. A radio communication device, more particularly for theGPS, DCS/PCS, UMTS and Bluetooth domain, characterized by an antenna asclaimed in claim 1.